Abstract: Based on more than 2 years' investigation in a fixed farm ecosystem, lincar program models for each stage of the evolution of farm ceosystcms, i.e., Grain-Mulberry (G-M) Grain-Mulberry-Fish (G-M-F)——Grain-Mulberry-Fish-Rabbit (G-M-F-R), were established According to the solution to the models, calculation of shadow prices fensibility analysis of improving major constraints and simulation of the effect of improved ranges of constraints on the function of whole ecosystem, optimized designs were proposed and good results were achieved after their applying to the farms.

Key words: Wetland ecosystem, Distribution characteristics of phosphorus and potassium, Seasonal dynamics, Sanjiang Plain